Av (Hebrew: אָב‎‎, StandardAvTiberianʾĀḇAramaic אבאAbba; from Akkadianabu; "father") is the eleventh month of the civil year and the fifth month of the ecclesiastical year on the Hebrew calendar. The name is Babylonian in origin and appeared in the Talmud around the 3rd century. This is the only month which is not named in the Bible. It is a summer month of 30 days. Av usually occurs in July–August on the Gregorian calendar.

The Babylonian Talmud, Taanit 29a, states that "when we enter [the month of] Av, our joy is diminished". This is because the darkest events in Jewish history occurred during the first week and a half of this month, particularly The Nine Days which culminate in Tisha B'Av, the 9th of Av. However, there is a minor and largely unknown holiday during the full moon of the month called Tu B'Av which was, in ancient times, one of the happiest days of the year.

The month is also sometimes referred to as Menachem Av (Hebrew: מנחם אב‎‎) (Av of Comfort or Comforter of Father(s)), but most only use this title in the sanctification of the month recited on the Shabbat before Rosh Chodesh and following Tisha B'Av.

15 Av - The Day of the Breaking of the Ax - when the Holy Temple existed, the cutting of firewood for the altar was completed on this date every year. The event was celebrated by feasting, rejoicing, and the ceremonial breaking of the axes.[citation needed]

In the story of Xenogears, Av is the name of a country, named after the Hebrew month. In the official Japanese version translation, however, it was transliterated Ave. This was later further changed by the translation process to Aveh for the English version.